I just went back and put one in. Here is another brand. This is the one I bought for blacking screws at work. It's just over $100 a gallon (minimum quantity), though they will send a sample if you pay the shipping fee. I suspect, from the descriptions, that this is where Caswell (my first link) is getting theirs and then is repackaging it into smaller containers. EPI also makes a mil-spec hot stainless blacking chemistry for those with bluing tanks.